1. Field of the Invention
The present invention relates to a power-line-operated high-frequency power-limited lighting system, especially as applicable in a suspended ceiling system.
2. Description of Prior Art
A power-limited high-frequency lighting system is described in U.S. Pat. No. 4,293,799 to Roberts. However, that lighting system is specifically intended for safely operating relatively low-power low-output fluorescent lamps/luminaires in situations involving a hazardous atmosphere, such as in a coal mine, and is not suitable for general lighting applications for the following reasons.
i) The Roberts system provides for series-connection of a number of luminaires (typically five), all powered from a single power-limited output of a power supply. Thus, if one of these luminaires were to become disconnected, such as by removal or by breakage, all the other series-connected luminaires would lose power and become inoperable.
ii) The Roberts system is not suitable for operation with its power supply left unloaded in that the power supply would then dissipate an excessive amount of power, namely more than all the power that otherwise would be used by all the series-connected luminaires when operating at full power.
iii) The amount of light provided from each luminaire in the Roberts system--being only on the order of a few hundred Lumens--is entirely too low to be effective for general illumination.
iv) Roberts provides for an individual power-line-operated inverter for each power-limited output, i.e. for each set of series-connected luminaires, a practice that is non-conducive to achieving cost-effectivity in lighting systems for general lighting applications.
v) Due to the particular method of voltage-limiting used in the power supply of the Roberts system, each power-limited output can not be used to the full limit of the power level that otherwise would be safe to use.
Rationale Related to the Invention
Due to potential fire hazards, presently used power-line-operated ceiling lighting fixtures can not conveniently and safely be installed by persons of but ordinary skills. Moreover, the wiring means required for safe installation is relatively costly to acquire and cumbersome to install.
On the other hand, if lighting fixtures could be powered by way of so-called Class 2 or Class 3 electrical circuits (for definition of such circuits, see Section 725 of the National Electrical Code 1984), they could indeed be made such as to be conveniently and safely installed by persons of but ordinary skills.
However, the output of Class 2 or Class 3 circuits (hereinafter: Class-2/3 circuits) is strictly limited in maximum rated Volt-Amperes (100 VA) and would appear not to yield enough power to provide an amount of illumination that would be considered adequate in most ordinary lighting installations.
Yet, within its maximum Volt-Amp rating, a Class 2/3 circuit does have enough power potentially available to provide for an amount of illumination that is nearly equal to that normally obtained from one of the commonly used four-lamp fluorescent ceiling fixtures.
Hence, if means were provided by which such ceiling fixtures could each individually be powered by way of a Class 2/3 power source, a very safe and easy-to-install and simple-to-modify ceiling lighting system might result.
Against this background, it would seem useful to provide for a Power-Limited Ceiling Lighting System; which is indeed the overall object of the instant invention.